Abnormal Detection System for Balancer and Abnormal Detection Method for Balancer

Abstract

The present invention provides an abnormality detection system for a balancer and an abnormality detection method for a balancer. An abnormality occurring in the balancer can be easily detected. The system includes: a robot; a motor that moves the robot; a balancer that is provided on the robot and generates an auxiliary torque for assisting the power of the motor by the force generated by an elastic body; and a control device that, during the standby of the robot, measures the current value of the motor that operates to keep the robot in a posture, and detects an abnormality of the balancer by comparing the current value with the current command value of the motor required to keep the robot in a posture.

Description

Technical Field

[0001] The present invention relates to an abnormality detection system for a balancer and an abnormality detection method for a balancer. Background Art

[0002] Conventionally, in a multi-joint robot, a balancer has been used to assist the power of a servo motor that drives an axis on which a load generated by gravity acts, by generating a force in a direction opposite to the load generated by gravity (for example, refer to Patent Document 1).

[0003] The balancer generates a force for assisting the power of the servo motor by the force generated by an elastic body. As the elastic body, a gas spring that generates an elastic force (repulsive force) by compression of gas, a spring such as a coil spring, etc. are known. Hereinafter, a balancer that uses a gas spring as the elastic body may be referred to as a gas balancer, and a balancer that uses a spring as the elastic body may be referred to as a spring balancer.

[0004] Prior art documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2019-98413 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] Generally, a collision detection function is provided in a system equipped with a multi-joint robot. The collision detection function is to calculate, during the operation of the robot, the difference between the current command value of the servo motor required to execute the operation plan of the robot and the current value of the servo motor actually required to operate the robot at a prescribed control cycle as an estimated disturbance value, and when this estimated disturbance value exceeds a prescribed threshold value, it is determined that the robot has collided with some object.

[0009] For example, when an abnormality such as breakage of a spring occurs in a spring balancer, the force (torque) of the spring balancer for assisting the operation of the motor becomes smaller, so the current value when the servo motor actually operates is larger than the current command value supplied to the servo motor. Thus, it can be considered that, similarly to when performing collision detection, by comparing the estimated disturbance value with the threshold value, an abnormality of the spring balancer can be detected.

[0010] However, in order to prevent false detection in the case where the robot moves with large acceleration and deceleration actions, or in the case where the robot moves in a state where it greatly deviates from a preset load, for example, a certain margin is set for the threshold value used to determine the occurrence of a collision in the collision detection function. This margin is set to be greater than the amount of change in the torque of the motor caused by an abnormality in the balancer. That is, the change in the torque of the motor caused by an abnormality in the balancer is smaller than the change in the torque of the motor caused by a collision during the movement of the robot. Therefore, it is difficult to detect an abnormality in the balancer through the collision detection function. Therefore, it is desirable to be able to easily detect whether an abnormality has occurred in the balancer.

[0011] Solutions for solving the problems

[0012] An abnormality detection system for a balancer according to one aspect of the present disclosure includes: a robot; a motor that moves the robot; a balancer that is provided on the robot and generates an auxiliary torque for assisting the power of the motor by the force generated by an elastic body; and a control device that, during standby of the robot, measures the current value of the motor that operates to keep the robot in a posture, and detects an abnormality in the balancer by comparing the current value with the current command value of the motor required to keep the robot in a posture.

[0013] An abnormality detection method for a balancer according to one aspect of the present disclosure is an abnormality detection method for a balancer provided on a robot that is operated by a motor and generates an auxiliary torque for assisting the power of the motor by the force generated by an elastic body. During standby of the robot, the current value of the motor that operates to keep the robot in a posture is measured, and an abnormality in the balancer is detected by comparing the current value with the current command value of the motor required to keep the robot in a posture.

[0014] Effects of the invention

[0015] According to one aspect, it is possible to easily detect whether an abnormality has occurred in the balancer. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a diagram showing the structure of an abnormality detection system for a balancer according to one aspect of the present disclosure.

[0017] Figure 2 is a diagram showing the internal structure of the balancer.

[0018] Figure 3 is a graph for explaining the change in the torque of the motor accompanying an abnormality in the balancer.

[0019] Figure 4It is a graph showing the change in the estimated interference value when the balancer is normal and when the balancer is abnormal.

[0020] Figure 5 It is a flowchart showing the collision detection operation of the robot and the abnormality detection operation of the balancer.

[0021] Explanation of reference signs

[0022] 1: Abnormality detection system of the balancer; 2: Robot; 26: Servo motor; 3: Balancer; 33, 34: Helical springs (elastic bodies); 4: Control device; TH2: Second threshold (threshold for balancer abnormality detection). Detailed implementation mode

[0023] Next, a mode of the present disclosure will be described in detail with reference to the drawings.

[0024] As Figure 1 shown, the abnormality detection system 1 of the balancer includes a robot 2, a balancer 3, and a control device 4 that controls the robot 2.

[0025] The robot 2 has: a base portion 21 fixed to the ground; a rotating portion 22 supported by the base portion 21 so as to be rotatable about a vertical first axis X1 relative to the base portion 21; a first arm portion 23 rotatable about a horizontal second axis X2 relative to the rotating portion 22; a second arm portion 24 rotatable about a third axis X3 at the tip of the first arm portion 23; and a wrist unit 25 supported at the tip of the second arm portion 24. A servo motor 26 that moves the first arm portion 23 is disposed inside the first arm portion 23.

[0026] The balancer 3 is provided between the rotating portion 22 and the first arm portion 23 of the robot 2. As Figure 2 shown, the balancer 3 shown in the present embodiment is a spring balancer in which two helical springs 33, 34 as elastic bodies are accommodated inside a housing 31. A rod portion 32 is provided inside the housing 31, and the tip portion 32a of the rod portion 32 projects outside the housing 31. A stopper portion 35 is attached to the rear end portion 32b of the rod portion 32 disposed inside the housing 31.

[0027] The elastic constants of the helical spring 33 and the helical spring 34 are different. The diameter of the helical spring 33 is larger than the diameter of the helical spring 34, and the helical spring 33 is disposed on the outer periphery of the helical spring 34. The helical springs 33, 34 are coaxially disposed on the outer periphery of the rod portion 32. The helical springs 33, 34 are attached within a range between the inner wall surface 31a disposed on the tip portion 32a side of the rod portion 32 of the housing 31 and the stopper portion 35. The helical springs 33, 34 apply a force to the rod portion 32 in a direction to retract into the housing 31 by means of the stopper portion 35.

[0028] The housing 31 of the balancer 3 is mounted on the rotating part 22 of the robot 2, and the top part 32a of the rod part 32 of the balancer 3 is mounted on the first arm part 23 of the robot 2. The balancer 3 generates an auxiliary torque that assists the power of the servo motor 26 by the force generated by the coil springs 33 and 34 as elastic bodies. The servo motor 26 is a motor that moves the first arm part 23 on which a large load generated by gravity acts. Thus, the balancer 3 functions to reduce the load on the servo motor 26 or resist the movement of the first arm part 23 according to the movement of the first arm part 23.

[0029] The control device 4 controls the robot 2 to perform various actions by providing a current command value to the servo motor 26 of the robot 2. In addition, the control device 4 has a collision detection function for detecting whether the robot 2 has collided with an external object and a balancer abnormality detection function for detecting an abnormality of the balancer 3.

[0030] The collision detection function of the control device 4 is executed during the movement of the robot 2. The movement of the robot 2 means a state in which the robot 2 is performing a prescribed robot action through the cooperation of the rotating part 22, the first arm part 23, the second arm part 24, and the wrist unit 25. The control device 4 that executes the collision detection function calculates, during the movement of the robot 2, the difference between the current command value (torque command value) provided to the servo motor 26 and the current value (actual torque value) of the servo motor 26 at a prescribed control cycle as an estimated disturbance value. The current value (actual torque value) of the servo motor 26 is a value actually detected when the robot 2 moves based on this current command value. The control device 4 compares the calculated estimated disturbance value with a prescribed first threshold value TH1 for collision detection, and determines that the robot 2 has collided with an external object when the estimated disturbance value exceeds the first threshold value TH1.

[0031] The balancer abnormality detection function of the control device 4 is executed while the robot 2 is on standby. The standby state of the robot 2 means a state in which the robot 2 stops at a prescribed standby position during the period from the end of a series of robot actions until the start of the next series of robot actions. The servo motor 26 also always operates while the robot 2 is on standby to generate a prescribed torque on the first arm part 23 to hold the first arm part 23 in a prescribed posture.

[0032] Here, as Figure 3 shown, a main torque Ts generated by the servo motor 26 and an auxiliary torque Tb generated by the coil springs 33 and 34 of the balancer 3 act on the first arm part 23 of the robot 2 equipped with the balancer 3 at the same time, and a necessary torque Tr for moving the robot 2 is provided. In Figure 3In (A), the torque distribution in the case where the balancer 3 functions normally is shown, and in (B), the torque distribution in the case where an abnormality has occurred in the balancer 3 is shown.

[0033] Since the balancer 3 functions in a manner that reduces the load on the servo motor 26 that moves the first arm portion 23, the necessary torque Tr for moving the first arm portion 23 is the sum of the main torque Ts generated by the servo motor 26 and the auxiliary torque Tb generated by the balancer 3. When an abnormality such as breakage occurs in the coil springs 33 and 34 of the balancer 3, the auxiliary torque Tb generated by the balancer 3 decreases as shown in (B) of Figure 3 . Therefore, in order to ensure the necessary torque Tr, it is necessary to increase the main torque Ts of the servo motor 26 (increase the current value of the servo motor 26).

[0034] The torque increase amount ΔTs of the servo motor 26 at this time corresponds to the torque decrease amount of the balancer 3. That is, when the torque increase amount ΔTs exceeds a specified magnitude, it can be determined that some abnormality such as breakage of the coil springs 33 and 34 has occurred in the balancer 3. However, the torque increase amount ΔTs is smaller than the torque fluctuation amount that normally occurs when the robot 2 operates.

[0035] Figure 4 The change in the estimated disturbance value when the balancer 3 is normal (indicated by a solid line) and when it is abnormal (indicated by a dashed line) is shown. As shown in Figure 4 , even when the estimated disturbance value is calculated by the collision detection function of the control device 4, sometimes there is no clear difference in the estimated disturbance value during the operation of the robot 2 between when the balancer 3 is normal and when it is abnormal, making it difficult to determine the abnormality of the balancer 3.

[0036] Therefore, the control device 4 executes the balancer abnormality detection function during the standby of the robot 2. As shown in Figure 4 , during the standby of the robot 2, a clear difference appears between when the balancer 3 is normal (indicated by a solid line) and when it is abnormal (indicated by a dashed line). Thus, the control device 4 that executes the balancer abnormality detection function compares the current command value (torque command value) supplied to the servo motor 26 with the actually detected current value (actual torque value) of the servo motor 26 that keeps the robot 2 in a posture at a specified control cycle during the standby of the robot 2, thereby detecting the abnormality of the balancer 3.

[0037] Specifically, the control device 4 calculates the difference between the current command value of the servo motor 26 and the current value of the servo motor 26 as the estimated disturbance value. The current command value of the servo motor 26 is the value required to keep the robot 2 in a standby posture, and the current value of the servo motor 26 is the value actually detected when the servo motor 26 is driven based on this current command value to make the robot 2 perform a posture holding action. The control device 4 compares the calculated estimated disturbance value with a prescribed second threshold value TH2 for balancer abnormality detection. When the estimated disturbance value exceeds the second threshold value, it is determined that an abnormality has occurred in the balancer 3. The second threshold value TH2 for balancer abnormality detection is set to a value capable of detecting a decrease in the auxiliary torque Tb caused by an abnormality in the balancer 3. As Figure 4 shown, this second threshold value TH2 is set to a value that is larger than the estimated disturbance value during standby of the robot 2 when the balancer 3 is normal, but is very small compared to the first threshold value TH1 for collision detection.

[0038] Next, the specific operation of the balancer abnormality detection system 1 configured in this way will be described with reference to the Figure 5 flowchart shown.

[0039] The control device 4 supplies a prescribed current command value to the servo motor 26 of the robot 2 according to a prescribed operation program to make the robot 2 operate. After the robot 2 starts operating, the control device 4 monitors whether the robot 2 is in a standby state (S101).

[0040] When the robot 2 is not in a standby state in step S101, that is, when the robot 2 is in an operating state (step S101: "No"), the control device 4 measures and acquires the current value of the servo motor 26 at a prescribed control cycle (S102). After that, the control device 4 calculates the estimated disturbance value (S103), which is the difference between the acquired current value and the current command value supplied to the servo motor 26 required to make the robot operate.

[0041] The control device 4 compares the calculated estimated disturbance value with the first threshold value TH1 for collision detection and determines whether the estimated disturbance value exceeds the first threshold value TH1 (S104). When the estimated disturbance value does not exceed the first threshold value TH1 in step S104 (step S104: "No"), the control device 4 returns the process to step S101.

[0042] When the estimated disturbance value exceeds the first threshold value TH1 in step S104 (step S104: "Yes"), the control device 4 determines that the robot 2 has collided with an external object and notifies the collision determination of the robot 2 (S105). The notification of the collision determination of the robot 2 is, for example, as shown in Figure 1The display for notifying that a collision has occurred to the robot 2 is performed in the monitor screen 41 provided in the control device 4 as shown.

[0043] When the robot 2 is in a standby state in step S101 (step S101: "Yes"), the control device 4 measures and acquires the current value of the servo motor 26 at a prescribed control cycle (S106). After that, the control device 4 calculates an estimated disturbance value (S107), which is the difference between the acquired current value and the current command value to be provided to the servo motor 26 for keeping the robot 2 in a posture.

[0044] The control device 4 compares the calculated estimated disturbance value with a second threshold TH2 for balancer abnormality detection, and determines whether the estimated disturbance value exceeds the second threshold TH2 (S108). When the estimated disturbance value does not exceed the second threshold TH2 in step S108 (step S108: "No"), the control device 4 returns the process to step S101.

[0045] When the estimated disturbance value exceeds the second threshold TH2 in step S108 (step S108: "Yes"), the control device 4 determines that some abnormality such as breakage of the coil springs 33 and 34 has occurred in the balancer 3, and notifies the abnormality determination of the balancer 3 (S109). The notification of the abnormality determination of the balancer 3 is, for example, as Figure 1 The display for notifying that there is an abnormality in the balancer 3 is performed in the monitor screen 41 provided in the control device 4 as shown.

[0046] In this way, according to the balancer 3 abnormality detection system 1 and the abnormality detection method, there are provided: a robot 2; a servo motor 26 that moves the robot 2; a balancer 3 that is provided on the robot 2 and generates an auxiliary rotation that assists the power of the servo motor 26 by the force generated by an elastic body (coil springs 33 and 34); and a control device 4 that, when the robot 2 is in standby, measures the current value of the servo motor 26 that operates to keep the robot 2 in a posture, and detects an abnormality of the balancer 3 by comparing the current value with the current command value of the servo motor 26 required to keep the robot 2 in a posture. Therefore, an abnormality of the balancer 3 can be reliably detected at an early stage.

[0047] In addition, the control device 4 has a second threshold value TH2. During the standby of the robot 2, an estimated disturbance value, which is the difference between the current value and the current command value, is calculated. When the estimated disturbance value exceeds the second threshold value TH2, it is determined that the balancer 3 is abnormal. Here, the second threshold value TH2 is set to a value capable of detecting a decrease in the auxiliary torque caused by the abnormality of the balancer 3. Therefore, by simply newly storing the second threshold value TH2 in the control device 4, it is possible to easily construct a system capable of easily detecting the abnormality of the balancer 3 by using the collision detection function of the control device 4.

[0048] The balancer 3 is not limited to a spring balancer that uses the coil springs 33 and 34 as elastic bodies. The elastic body may also be a spring other than the coil spring. In addition, the balancer 3 may be a gas balancer that uses a gas spring as the elastic body.

Claims

1. An abnormality detection system for a balancer, comprising: A robot; A motor that moves the robot; A balancer that is provided on the robot and generates an auxiliary torque that assists the power of the motor by the force generated by an elastic body; and A control device that, while the robot is on standby, measures the current value of the motor actually detected when operating to keep the robot in a posture, and detects an abnormality of the balancer by comparing the current value with a current command value supplied to the motor as a command value of the current required to keep the robot in a posture when the balancer is normal.

2. The abnormality detection system for a balancer according to claim 1, wherein the control device has a threshold value for detecting an abnormality of the balancer, and while the robot is on standby, calculates the difference between the current value and the current command value, and determines that the balancer is abnormal when the difference exceeds the threshold value, wherein the threshold value for detecting an abnormality of the balancer is set to a value capable of detecting a decrease in the auxiliary torque caused by an abnormality of the balancer.

3. An abnormality detection method for a balancer, the balancer being provided on a robot that is operated by a motor and generating an auxiliary torque that assists the power of the motor by the force generated by an elastic body. In the abnormality detection method for the balancer, while the robot is on standby, measures the current value of the motor actually detected when operating to keep the robot in a posture, and detects an abnormality of the balancer by comparing the current value with a current command value supplied to the motor as a command value of the current required to keep the robot in a posture when the balancer is normal.

4. The abnormality detection method for a balancer according to claim 3, wherein while the robot is on standby, calculates the difference between the current value and the current command value, and determines that the balancer is abnormal when the difference exceeds a threshold value for detecting an abnormality of the balancer, wherein the threshold value for detecting an abnormality of the balancer is set to a value capable of detecting a decrease in the auxiliary torque caused by an abnormality of the balancer.

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